Scaled deployment of Wolbachia to protect the community from dengue and other Aedes transmitted arboviruses

Abstract

Background: A number of new technologies are under development for the control of mosquito transmitted viruses, such as dengue, chikungunya and Zika that all require the release of modified mosquitoes into the environment. None of these technologies has been able to demonstrate evidence that they can be implemented at a scale beyond small pilots. Here we report the first successful citywide scaled deployment of Wolbachia in the northern Australian city of Townsville. Methods: The wMel strain of Wolbachia was backcrossed into a local Aedes aegypti genotype and mass reared mosquitoes were deployed as eggs using mosquito release containers (MRCs). In initial stages these releases were undertaken by program staff but in later stages this was replaced by direct community release including the development of a school program that saw children undertake releases. Mosquito monitoring was undertaken with Biogents Sentinel (BGS) traps and individual mosquitoes were screened for the presence of Wolbachia with a Taqman qPCR or LAMP diagnostic assay. Dengue case notifications from Queensland Health Communicable Disease Branch were used to track dengue cases in the city before and after release. Results: Wolbachia was successfully established into local Ae. aegypti mosquitoes across 66 km ² in four stages over 28 months with full community support. A feature of the program was the development of a scaled approach to community engagement. Wolbachia frequencies have remained stable since deployment and to date no local dengue transmission has been confirmed in any area of Townsville after Wolbachia has established, despite local transmission events every year for the prior 13 years and an epidemiological context of increasing imported cases. Conclusion: Deployment of Wolbachia into Ae. aegypti populations can be readily scaled to areas of ~60km ² quickly and cost effectively and appears in this context to be effective at stopping local dengue transmission.

Keywords: Aedes aegypti; Dengue; Eliminate Dengue; World Mosquito Program; community engagement; mosquito release.

Figure 1.. Release site.

Map of Townsville city showing the boundaries of the four release stages.

Figure 2.. Release containers.

Photos illustrating different mosquito release containers used in the deployment. ( A) Bucket mosquito release containers (MRCs) used in stage 1 releases ( B) Clear bucket MRC used in Wolbachia Warriors school program in stage 1 ( C) Mozzie Box MRC that was used in stages 2–4 ( D) Material given to school children as part of the Wolbachia Warriors program.

Figure 3.. Wolbachia establishment by suburb.

For each stage ( A– D) and suburb Wolbachia frequency is plotted against time. Yellow shading indicates periods when releases were undertaken. Bars show the number of mosquitos captured in Biogents Sentinel (BGS) traps and tested for Wolbachia.

Figure 4.. Dengue case notifications.

Dengue case notifications per month in Townsville, Australia, January 2001 – March 2019, before and after Wolbachia mosquito deployments. Notifications include laboratory-confirmed and probable dengue cases, classified as locally-acquired ( A) or imported ( B) based on a history of overseas travel to a dengue-affected country during the period 3 – 12 days prior to illness onset. Data was extracted from the Queensland Health Notifiable Conditions System (NOCS) on 11 April 2019. Green shading shows the four stages of Wolbachia deployment conducted in Townsville since October 2014.